Sorry, but I forgot to mention that yes, the wave washer puts a spring like tension on the shifting linkage when attached to the shift levers (at both the transmission and shifter) to prevent the linkage from "rattling" around.
Install all 6 wave washers and the rattling noise you hear should disappear.
'66 Ragtop, vibrant red, 289-4V, 4-speed toploader
'68 Fastback, space blue metalic, 351C-4-V, 4-speed toploader
'69 Mach I, (Pending Resto Project)
'66 Fastback (because I wanted one)